Epidemiology refers to the branch of medicine that deals with the study of the causes, distribution, and control of disease in populations. In this section we will discuss the most commonly diagnosed and most fatal types of cancer in the United States.

Cancer Risk

By far, the number one risk factor for cancer (indeed for virtually all chronic diseases) is age. Approximately 77% of all cancers are diagnosed in people 55 years of age or older. Cancer researchers describe the risk of cancer in a number of ways:

Lifetime risk
refers to the probability that any one person will develop cancer in his or her lifetime. For example, in the United States, the lifetime risk of developing cancer for men is less than one in two. In women, it is approximately one in three.

Relative risk
measures the degree of the relationship between a particular risk factor and a particular cancer. Relative risk is expressed as a ratio of the number of cancer cases in a group of individuals with a risk factor over the number of cases in those without it. Most relative risks are small. For example, women who have a mother, sister, or daughter with breast cancer have about a 2-fold increased risk of developing breast cancer compared to women with no such family history of breast cancer.

Some risk factors are associated with multiple cancers (eg, tobacco and diet), while other risk factors are specific to one type of cancer (eg, ultraviolet radiation and skin cancer, human papillomavirus and cervical cancer). To learn more about the individual risk factors for a particular type of cancer, click on the cancer of your choice at the bottom of this page.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

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